docs: def K_butterfly_valve_Crane(D, fd=None, style=0):
      r'''Returns the loss coefficient for a butterfly valve as shown in
      [1]_. Three different types are supported; Centric (`style` = 0),
      double offset (`style` = 1), and triple offset (`style` = 2).
          
      .. math::
          K = N\cdot f_d
          
      N is obtained from the following table:
          
      +------------+---------+---------------+---------------+
      | Size range | Centric | Double offset | Triple offset |
      +============+=========+===============+===============+
      | 2" - 8"    | 45      | 74            | 218           |
      +------------+---------+---------------+---------------+
      | 10" - 14"  | 35      | 52            | 96            |
      +------------+---------+---------------+---------------+
      | 16" - 24"  | 25      | 43            | 55            |
      +------------+---------+---------------+---------------+
          
      The actual change of coefficients happen at <= 9" and <= 15".
              
      Parameters
      ----------
      D : float
          Diameter of the pipe section the valve in mounted in; the
          same as the line size [m]
      fd : float, optional
          Darcy friction factor calculated for the actual pipe flow in clean 
          steel (roughness = 0.0018 inch) in the fully developed turbulent 
          region; do not specify this to use the original Crane friction factor!,
          [-]
      style : int, optional
          Either 0 (centric), 1 (double offset), or 2 (triple offset) [-]
  
      Returns
      -------
      K : float
          Loss coefficient with respect to the pipe inside diameter [-]
  
      Notes
      -----    
      This method is not valid in the laminar regime and the pressure drop will
      be underestimated in those conditions.
  
      Examples
      --------
      >>> K_butterfly_valve_Crane(D=.1, style=2)
      3.5508841974793284
      
      References
      ----------
      .. [1] Crane Co. Flow of Fluids Through Valves, Fittings, and Pipe. Crane,
         2009.
      '''
      if fd is None:
          fd = ft_Crane(D)
      try:
          c1, c2, c3 = butterfly_valve_Crane_coeffs[style]
      except KeyError:
          raise KeyError('Accepted valve styles are 0 (centric), 1 (double offset), or 2 (triple offset) only.')
      if D <= 0.2286:
          # 2-8 inches, split at 9 inch
          return c1*fd
      elif D <= 0.381:
          # 10-14 inches, split at 15 inch
          return c2*fd
      else:
          # 16-18 inches
          return c3*fd